1. Field of the Invention
This invention concerns the manufacture of contact lenses and more particularly relates to the machining of contact lenses from stock material which is secured and accurately positioned within a supporting mold having an outer surface which complements an inner surface of a collet.
2. Description of the Prior Art
Contact lenses are produced by a variety of techniques including spincasting, lathing the lens from button-shaped stock material, fully molding the lens, or casting one surface of the lens within a mold and then machining the second surface following polymerization of the lens. When using the latter method, it is necessary to support the polymerizing vessel or casting mold in a lathe for subsequent machining of the exposed face of the lens. Regardless of which method is employed, a machining operation is frequently required for edging, diameter cutting or polishing the lenses.
Heretofore, the lens molds were supported by positioning or clamping them into mechanical collets mounted in a lathe spindle. The collets typically included fingers, studs, posts, pillars and springs to hold and support the molds for lathing. However, these aforementioned supporting devices were not entirely suitable for accurately and precisely machining the lenses. Accuracy, as understood in the contact lens industry, refers to precise alignment of the lens material to ensure accurate centering of an optical surface, and proper thickness control to assure a correct and suitable lens thickness for use.
These earlier collets were usually mounted onto a lathe spindle and often a series of fingers or springs had to be manually moved while the operator inserted the mold. Even with spincast lenses, the molds had to be retained on center using collets. Variations from collet assembly to collet assembly caused variations and inconsistencies in the lenses.
Accordingly, there exists the need for a method and apparatus which facilitates mounting and supporting a lens mold within a collet so as to accurately align and center the mold and lens material during a machining operation.